Crystal Phase-dependent Electrochromic Performance of Porous Titanium Dioxide Nanotube Films

Electrochromic porous TiO2 nanotube films with different structural phases were successfully coated on fluorine-doped tin oxide (FTO) glasses by a doctor-blade method with subsequent post-annealing treatment. The TiO2 crystal phases can be easily tailored via simple post-annealing treatment. The electrochromic performance of coated films was found to be strongly dependent on the TiO2 crystal phase. An improved optical modulation range was obtained for TiO2(B) (28.1%) compared to TiO2 anatase (4.5%) and anatase/TiO2(B) mixed phases (10%) films by measuring in-situ optical transmittance measurement at 633 nm upon the polarized potential between -0.8V (colored state) and 1.0 V (bleached state). Moreover, the coloration efficiency of pure TiO2(B) nanotube films reached a value as high as 66.69 cm2/C at 633 nm. These results can be ascribed to the enhanced Li+ diffusion coefficient of the TiO2(B) nanotube film with its open framework structure, which can effectively facilitate the transport of Li+ ions during the coloring process. This work demonstrates great potential use of TiO2(B) films in large-scale electrochromic applications .